A system may use an image sensor for acquiring images of areas of a substrate. The images may be acquired during one or more processes such as but not limited to a manufacturing process, an inspection process, and the like.
The acquisition of an image may require positioning an image sensor at an exact distance from the substrate.
During the positioning process the entire substrate may be elevated or lowered in relation to the image sensor. The elevation or lowering of the entire substrate reduces the accuracy of the positioning process, increases the duration of the positioning process and may require applying substantial forces in the substrate.
Furthermore, in wafer inspection and review (also in production) it is extremely important to arrive at a position with very high accuracy in the order of 1 nm and remain still in that position during the image grab with ˜0.1 nm accuracy.
Any pitch or tilt error of the stage may result in a navigation error or vibrations during the image acquisition.
The reason for this is that the interferometer measures the distance to the stage at a plane that may be several mm below the wafer plane.
X and Y errors results that is equal to this lever H times the angular error in pitch or tilt.
For example, for a 10 mm lever and a 1 microradian tilt error, an X error would result that is equal to 10 nm.
There is a growing need to provide an effective positioning process.